Damage to protein synthesis concurrent with lipid peroxidation in rat liver slices: effect of halogenated compounds, peroxides, and vitamin E1

Protein synthesis and lipid peroxidation were evaluated in rat liver slices incubated in the presence of oxidants and protein synthesis inhibitors. Protein synthesis by rat liver slices was evaluated by [3H]leucine incorporation into the trichloroacetic acid (TCA)-insoluble material, and lipid peroxidation was evaluated by thiobarbituric acid-reactive substances (TBARS) released into the incubation medium. Protein synthesis inhibition by bromotrichloromethane (BrCCl3) or t-butyl hydroperoxide (t-BOOH) depended on the incubation time and oxidant concentration. [3H]Leucine incorporation was decreased to 20 and 47% of control values and TBARS were enhanced from the control value of 16.9 to 45.3 and 62.5 nmol/g of liver by incubation for 1 h with 1 mM BrCCl3 and t-BOOH, respectively. Following incubation, both protein synthesis damage and lipid peroxidation were decreased in control and oxidant-treated slices prepared from rats injected with 200 mg of DL-alpha-tocopherol/kg of body wt. Release of lactate dehydrogenase was not enhanced by oxidant treatment. Protein synthesis inhibitors reversibly decreased [3H]leucine incorporation, but the effect of oxidants on protein synthesis was irreversible. Cumene hydroperoxide and methyl ethyl ketone peroxide, but not hydrogen peroxide, damaged protein synthesis and induced lipid peroxidation. The ability of carbon tetrabromide, benzyl chloride, bromoform, bromobenzene, carbon tetrachloride, chloroform, dichloromethane, and bromochloromethane to inhibit protein synthesis was correlated with their ability to induce lipid peroxidation, and with their LD50. The results suggest that oxidant-induced lipid peroxidation and protein synthesis damage occurred concurrently, and that protein synthesis inhibition may be involved in cell injury or death mediated by free radicals.     

Right Internal Mammary Artery Implantation into Right Ventricular Myocardium for Revascularization of the Entire Heart: Experimental Data and Preliminary Report

The left internal mammary artery implant combined with epicardiectomy and free omental graft provides three extra-coronary sources of blood. This operation tested in dogs with 92% main-stem occlusion of three coronary arteries protected 75% of the animals. Applied clinically in over 100 patients, the operation resulted in 90% improvement. To obtain complete myocardial revascularization, the right internal mammary artery has been used as a fourth source of extra-coronary blood. In 57 animals, the right internal mammary arteries were implanted into the anterior walls of the right ventricle; in 80% this vessel formed anastomoses with the right coronary tree, and in 65% with the right and left coronary arteriolar systems. Six patients are described who underwent right internal mammary artery implantation; five of these in addition had the combined operation of left internal mammary artery implant, epicardiectomy and free omental graft. All patients had completely blocked right coronary arteries; in addition, five had advanced disease of the left coronary arterial tree.     

The origin of reaction specificity in serine hydroxymethyltransferase

Cytosolic serine hydroxymethyltransferase has been shown previously to exhibit both broad substrate and reaction specificity. In addition to cleaving many different 3-hydroxyamino acids to glycine and an aldehyde, the enzyme also catalyzes with several amino acid substrate analogs decarboxylation, transamination, and racemization reactions. To elucidate the relationship of the structure of the substrate to reaction specificity, the interaction of both amino acid and folate substrates and substrate analogs with the enzyme has been studied by three different methods. These methods include investigating the effects of substrates and substrate analogs on the thermal denaturation properties of the enzyme by differential scanning calorimetry, determining the rate of peptide hydrogen exchange with solvent protons, and measuring the optical activity of the active site pyridoxal phosphate. All three methods suggest that the enzyme exists as an equilibrium between "open" and "closed" forms. Amino acid substrates enter and leave the active site in the open form, but catalysis occurs in the closed form. The data suggest that the amino acid analogs that undergo alternate reactions, such as racemization and transamination, bind only to the open form of the enzyme and that the alternate reactions occur in the open form. Therefore, one role for forming the closed form of the enzyme is to block side reactions and confer reaction specificity.     

Oxidant-induced haemoprotein degradation in rat tissue slices: effect of bromotrichloromethane, antioxidants and chelators

Haemoprotein degradation and lipid peroxidation were evaluated in rat liver, kidney and heart slices incubated for 2 h in the presence and absence of bromotrichloromethane, antioxidants and chelators to obtain information about the relationship between oxidants and damage to haemoproteins. Haemoproteins were modified by bromotrichloromethane, and this modification, measured as loss of ferrohaemoproteins, generally was concurrent with lipid peroxidation measured as thiobarbituric acid-reactive substances. These two processes occurred simultaneously as a function of incubation time and oxidant concentration. Inhibition of the two processes by nordihydroguaiaretic acid, butylated hydroxyanisole and Trolox C, and lack of inhibition by mannitol, catalase and superoxide dismutase also were coincident. However, Methylene blue, EDTA, sodium fluoride, 2,4-dinitrophenol, N-ethylmaleimide and o-phenanthroline affected the two processes differently. The results suggested that haemoproteins may compete with other molecules for oxidant radicals, thus serving as protectors of cells against oxidant radicals. Products of haemoprotein degradation such as protein polymers, free amino acids and bilirubin may be indicators of in vivo oxidative stress.     

Nyssa talamancana (Cornaceae), an addition to the remanant Laurasian Tertiary flora of southern Central America

A new species,Nyssa talamancana, with fruits larger than those of any other, either living or fossil, is described from Costa Rica and Panama. In size, number of germination valves, and surface-sculpturing, its endocarps resemble those of the fossil assemblage more than those of the other living species. The occurrence of this distinctive new member of a definitely Laurasian family, in association with other endemic or nearly endemic Laurasian taxa, at wet mid-elevations lends credence to the idea that these forests harbor remnants of the really ancient flora of southern Central America.     

Oxidant-increased proteolysis in rat liver slices: effect of bromotrichloromethane, antioxidants and effectors of proteolysis

Proteolysis and lipid peroxidation were evaluated in rat liver slices incubated in the presence of the oxidant bromotrichloromethane and effectors of proteolysis. Proteolysis was evaluated by S-amino acids and lipid peroxidation by thiobarbituric acid-reactive substances (TBARS) released into the incubation medium. The increased release of S-amino acids by BrCl3C depended on incubation time and oxidant concentration. S-Amino acid release increased 30% over control value and TBARS increased from 22 to 124 nmol/g liver by incubation for 120 min with 1 mM BrCl3C. Release of S-amino acids and TBARS was decreased when liver slices were treated with nor-dihydroguaiaretic acid (NDG), butylated hydroxyanisole (BHA), Trolox C, or N,N'-diphenyl-1,4-phenylenediamine (DPPD) immediately prior to addition of oxidant, suggesting participation of lipid-soluble free radicals. Oxidant-induced release of S-amino acids but not of TBARS was decreased by mannitol, suggesting participation of hydroxyl radical or a species with similar reactivity; and by superoxide dismutase and catalase, suggesting participation of superoxide and hydrogen peroxide, respectively. The decrease of S-amino acid release by sodium fluoride, sodium arsenate, 2,4-dinitrophenol, chloroquine, leupeptin, phenylmethylsulfonyl fluoride, EDTA and o-phenanthroline was variable, suggesting the presence in liver of several proteases to remove oxidatively-modified proteins.     

Morphology and lactose synthesis in tissue culture of mammary alveoli isolated from lactating mice

Summary Mammary epithelial cells from lactating mice synthesize and secrete lactose in culture and retain many features of their in vivo morphology if mammary glands are only partially dissociated to alveoli, rather than completely dissociated to single cells. After 5 d in culture lactose synthesis by alveoli cultured on floating collagen gels is 10 to 20 times higher than in cultures of single cells on floating collagen gels. Moreover, mammary alveoli in culture retain sensitivity to lactogenic hormones; the synthesis of lactose by alveoli depends on the continued presence of insulin and either hydrocortisone or prolactin. In addition, within alveoli the original juxtaposition of constituent epithelial cells is retained, and cells are cuboidal and have many microvilli and fat droplets. In contrast, alveoli on attached gels flatten and lose their secretory morphology. These results indicate that the shape of the cells, presence of lactogenic hormones, and maintenance of epithelial:epithelial cell contacts are required for maintenance of mammary epithelial cell differentiation in culture. This research was supported by Grants CA-16392 and AG-02909 from the National Institutes of Health and Institutional Grant IN 119 from the American Cancer Society.     

Methane emissions reduce the radiative cooling effect of a subtropical estuarine mangrove wetland by half

The role of coastal mangrove wetlands in sequestering atmospheric carbon dioxide (CO₂) and mitigating climate change has received increasing attention in recent years. While recent studies have shown that methane (CH₄) emissions can potentially offset the carbon burial rates in low‐salinity coastal wetlands, there is hitherto a paucity of direct and year‐round measurements of ecosystem‐scale CH₄ flux (F_CH4) from mangrove ecosystems. In this study, we examined the temporal variations and biophysical drivers of ecosystem‐scale F_CH4 in a subtropical estuarine mangrove wetland based on 3 years of eddy covariance measurements. Our results showed that daily mangrove F_CH4 reached a peak of over 0.1 g CH₄‐C m^?2 day^?1 during the summertime owing to a combination of high temperature and low salinity, while the wintertime F_CH4 was negligible. In this mangrove, the mean annual CH₄ emission was 11.7 ± 0.4 g CH₄‐C m^–2 year^?1 while the annual net ecosystem CO₂ exchange ranged between ?891 and ?690 g CO₂‐C m^?2 year^?1, indicating a net cooling effect on climate over decadal to centurial timescales. Meanwhile, we showed that mangrove F_CH4 could offset the negative radiative forcing caused by CO₂ uptake by 52% and 24% over a time horizon of 20 and 100 years, respectively, based on the corresponding sustained‐flux global warming potentials. Moreover, we found that 87% and 69% of the total variance of daily F_CH4 could be explained by the random forest machine learning algorithm and traditional linear regression model, respectively, with soil temperature and salinity being the most dominant controls. This study was the first of its kind to characterize ecosystem‐scale F_CH4 in a mangrove wetland with long‐term eddy covariance measurements. Our findings implied that future environmental changes such as climate warming and increasing river discharge might increase CH₄ emissions and hence reduce the net radiative cooling effect of estuarine mangrove forests.     

Reconstructing marine plankton food web interactions using DNA metabarcoding

Knowledge of zooplankton in situ diet is critical for accurate assessment of marine ecosystem function and structure, but due to methodological constraints, there is still a limited understanding of ecological networks in marine ecosystems. Here, we used DNA‐metabarcoding to study trophic interactions, with the aim to unveil the natural diet of zooplankton species under temporal variation of food resources. Several target consumers, including copepods and cladocerans, were investigated by sequencing 16S rRNA and 18S rRNA genes to identify prokaryote and eukaryote potential prey present in their guts. During the spring phytoplankton bloom, we found a dominance of diatom and dinoflagellate trophic links to copepods. During the summer period, zooplankton including cladocerans showed a more diverse diet dominated by cyanobacteria and heterotrophic prey. Our study suggests that copepods present trophic plasticity, changing their natural diet over seasons, and adapting their feeding strategies to the available prey spectrum, with some species being more selective. We did not find a large overlap of prey consumed by copepods and cladocerans, based on prey diversity found in their guts, suggesting that they occupy different roles in the trophic web. This study represents the first molecular approach to investigate several zooplankton–prey associations under seasonal variation, and highlights how, unlike other techniques, the diversity coverage is high when using DNA, allowing the possibility to detect a wide range of trophic interactions in plankton communities.